Due to the Choose...
of Earth's mantle these plates are continuously being created and consumed at the plate boundaries.

  The more dense oceanic plate subducts under the less dense continental plate. Subducted plate melts due to heat and friction. Melted plate, now magma, rises up to the surface.

Explanation:

a). in this case, dh> 0 and sd> 0. if t becomes larger, the term "-tds" will become more negative. at some point, it is possible that -dts will be more negative than the dh is positive, and the reaction will become spontaneous. this is probably the correct answer, but you should look at all of the other possibilities and make sure of that.